Chrome-acetate complex tannage



March 1965 H. sPAHRKKs ETAL 3,174,817

CHROME-ACETATE COMPLEX TANUAGE Filed Oct. 27, 1961 2 Sheds-Sheet 1 FIG. 7

mmvrons:

HEINRICH SPAHRKAS, GUSTAV MAUTHE.

A TTOFPNEY March 1965 H. sPAHRKAs ETAL 3,17

CHROME-ACETATE COMPLEX TANUAGE Filed Oct. 27, 1961 2 Sheets-Sheet 2 PIC-7.2

INVENTORS.

HEINRICH SPAHRKA S, GUSTAV MAUTE.

ATTORNEY nited States Germany Filed Oct. 27, 1961, Ser. No. 148,245

Claims priority, application Germany, Oct. 28, 1969, F 32,434; Apr. 8, 1961, F 33,624 2 Claims. (Cl. 894.26)

The present invention relates to and has as its object a new and useful process for the preparation of chromium tanned leather.

Tanning with basic sulphates of trivalent chromium is conventionally carried out according to the following process:

After pickling, the initial tanning is carried out with small-particled low-basic chrome liquors, followed by buffering with alkalies (sodium carbonate, sodium brcarbonate, sodium sulphite, and the like) in order to increase the basicity and thus of the particle size and astringency. Finally, neutralisation of the shaved leather and the usual working processes follow.

The increase of the basicity during tanning is an especially important working process. The process requires special precautions and attention (see Gustavson, Handbuch Grassmann-Bergrnann, vol. ll/Z, pages 208/209). Also the so-called neutralisation of chrome leather requires great care since it influences, similar to basilication, the appearance and the tightness of the grain.

Hitherto, no process has been known to carry out the chrome tanning in a simple manner, especially with the elimination of basification and neutralisation, without impairing the quality of the final product. A replacement of basilication by using highly basic liquors in the second stage of the tanning only means a transformation of the basification into the stage where a portion of the stock liquor is rendered basic, thus not being a genuine ad vantage. Moreover, the use of highly basic liquors in the stage of initial tanning does not come into consideration (the disadvantages are described by Stather Gerbereichernie und Gerbereitechnologie 1957) page 445 Pickling which render the raw hide material acid, also gives rise to a decrease of the basicity during the initial tanning which must be compensated by the basification-process in the further tanning.

Surprisingly, it has now been found that basification as well as neutralising, and under certain circumstances even pickling, becomes unnecessary when tanning is carried out with powdered carefully dried chrornic sulphate compounds (i.e. dry powdered chromium sulphate) or highly concentrated chromic sulphate lyes (i.e. the concentrated chromium sulphate solution) having a least a content of chromium oxide and an optimum basicity and containing coordinatively bound water-soluble organic acid, especially acetic radicals, in a specified proportion with regard to chromium; these chromium complex compounds being added to the animal hides or leathers, with or without the tanning liquor, in the undissolved or undiluted state.

it has also been found that these chromium compounds possess an extremely strong masking eliect when they are used in the tanning process in a highly concentrated form as thickened chrome lyes or as powdered carefully dried chromium products. These chromium complex compounds possess, as has further been found, in this method of application the property of converting themselves during the tanning process due to the presence of the moisture of the hides or on account of the tanning liquor added, whereby the initially strongly masking effect gradually disappears and chromium compounds are formed which are fully effective in tanning. The most important factor of this process is the uniformity with which the tanning activity increases. The rate of this uniform process is controllable by the temperature and by the quantity of added water. Moreover, the later conversion process in the course of tanning may be accelerated by admixing sodium carbonate, sodium bicarbonate, sodium sulphite, etc., to the powdered chromium compounds.

This process according to the invention results in a very rapid diffusion of the initially strongly masked chromium complex compounds through the hide or leather. The ever self-increasing tanning efiect of the chromium compounds during the course of tanning eliminates the disadvantages brought about by the usual basification in the conventional processes. The tannings may be conducted at a hi' h basicity even from the start without showing the disadvantages, such as chrome stains on the surface of the leather, to be expected by tanning technologists, thus rendering the usual neutralisation after chrome tanning unnecessary. By appropriately conducting the tanning process (temperature, adjustment of basicity), very high amounts of chromium can be taken up and bound by the leather in extremely brief tanning times. Moreover, a surprisingly good distribution of chromium in the leather is attained by the process according to the invention.

Thus, by the tanning according to the invention chrome leather is obtained with excellent properties such as a full soft handle and excellent smoothness, quality and tightness of the grain, whilst avoiding completely or partially otherwise usual working proccsses such as pickling, basification and neutralising.

It is already known that tanning with powdered chromium sulphate compounds oilers advantages over conventional tanning with chrome stock solutions (of H. Spahrkas and H. Schmid, Bemerkungen ziir Anwendung gerbfertiger Chomprodukte, Zeitschrift Das Leder 10, No. 7, page 145, 1959). According to this process, the tanning effects described above cannot be attained since the masking effect brought about therein is not sufficient at the beginning of tanning.

The great distinction between the known and the new process is explained in greater detail by way of example of the acetate masking: it is already known that the acetate radical is considered as readily capable of forming complex-forming acid radical. In theory as well as in practice the view prevails that dead flat and hard leather result from tanning with acetate-masked chromium sulphate stock solutions. In contradistinction to the compounds of the new process, such chrome liquors have the character of over-masked chrome solutions even at slight overdoses (from 0.3 mol acetate per mol/chrome onwards) which they retain during ageing when diluted by the tanning liquor.

On the other hand, small additions of acetate (below 0 3 mol acetate per mol/chrome) are practically ineffectrve in usual tanning processes since such chrome liquors scarcely distinguish themselves from the character of unmasked chrome liquors. An acetate dosing based upon a chrome stock solution suitable for practice can scarcely be effected since already insignificant deviations of the concentration, temperature, ageing, etc., lead to strong variations of the masking degree and detrimentally influence the tanning process. The great difference between the known and the new process is simplest illustrated by FIGURE 1. In the figures the vertical axis indicates the flocculation point expressed in percent basicity whereas the horizontal axis indicates the time of ageing in hours.

Curve 1 illustrates a conventional chrome sulphate stock solution (6% Cr O 33% basicity), curve 2 illustrates a chrome sulphate stock solution as 1 but boiled with 0.2 mol sodium acetate/ atom chrome, curve 3 illustrates chrome sulphate lye at 33% basicity, thickened to 3 18% Cr O treated with 0.2 mol sodium acetate/atom chrome and dried under mild conditions; and curve 4 illustrates a chrome sulfate product as 3 but without addition of sodium acetate.

The flocculation points have been established in percentages basicity upon dissolving or diluting in the cold state to 2.6% chromium oxide in various ageing stages by titrating 100 ml. of chrome solution with 3 N sodium carbonate. The ageing temperature is 30 C. The titration rate is 2 ml. feed in seconds.

Curve 1 represents the type of a conventional unmasked chromium sulphate stock solution at 33% basicity. Curve 2 shows a chromium sulphate stock solution boiled with 0.2 mol acetate-atom chrome. Both curves show later during ageing the same character of curve and differ in the flocculation point only immaterially. Fundamentally different is the course of curve 3 which likewise represents a chromium sulphate solution treated with 0.2 mol acetate/atom chrome, which, however, is thickened to 18% chromium oxide prior to ageing, or subsequently concentrated to chromium oxide by mild drying. In contradistinction to the chromium compounds of curve 1 and 2 the chromium compounds of curve 3 show at the start of ageing an extremely strong masking which continuously decreases and disappears completely after a few hours. Curve 4 shows the eifect of a sulphate masking proper (without use of acetate), the course being similar to that of curve 3. However, the fact becomes surprisingly apparent that the acetate amount practically ineffec tive in other conventional systems (curve 2) gives rise to a considerable intensification of the initial masking, the state at the end of 6 hours being the same.

It has further been found that for each masking acid radical or each combination of such acid radicals, the optimum amount required for the aforesaid tanning course is a typical value which may substantially deviate from the indicated optimum acetate amount.

In addition to water-soluble monocarboxylic acids such as acetic acids, Water-soluble dicarboxylic acids and watersoluble hydroxy-carboxylic acids are found suitable for the purpose of the invention.

Especially suitable are the free acids or the salts of acetic acid, formic acid, oxalic acid, glycollic acid and sulphophthalic acid. The FIGURE 2 shows the quantitative dilferences between the formate masking and acetate masking by way of example. Curve 1 shows the desired type of a chromium sulphate solution treated with 0.2 mol acetate/ atom chrome thickened to a content of 18% chromium oxide, or concentrated to about 25% chromium oxide by mild drying. In contradistinction to curve 1, curve 2 which shows an analogous chromium sulphate solution solution but treated with 0.2 mol formate/ atom chrome has an essentially flatter course of curve. In order to attain the desired high initial masking also with formate, essentially higher amounts are required as can be seen from curve 3 with an addition of 0.6 mol formate/ atom chrome. However, an increase of the formate quantity by a further 0.4 mol/atom chrome to 1.0 mol/ atom chrome already leads to overmasked chromium compounds which cannot be determined by titration and do not lead to fully tanning-active compounds in the course of the tanning process,

Curve 1 illustrates a chromium sulphate lye at 33% basicity thickened to 18% Cr O treated with 0.2 mol sodium acetate/ atom chrome and dried under mild conditions (identical with curve 3 of FIGURE 1). Curve 2 illustrates a chromium sulphate product as 1 but with addition of 0.2 mol sodium formate/atom chrome and curve 3 illustrates the chromium sulphate product as 1 but with addition of 0.6 mol sodium formate/atom chrome.

The chromium complex compounds required for this process are produced in the simplest manner by reacting chromic sulphate lyes thickened to a content of at least 15% chromium oxide, with the inventively used watersoluble organic acids or alkali metal salts thereof at an elevated temperature, or drying under mild conditions the chrome lyes treated with the indicated amounts of masking agents, provided they are powdered products.

The new tanning process is valuable for the full chrome tanning of pelts as Well as for chrome pretarmings for leather to be tanned in a combined manner and for aftertannings, also in combination with other after-tanning agents.

Example 1 100 parts by weight of calf pelts are drummed in a tumbler for 6 hours, after preliminary work usually carried out for upper leather (liming, de-liming, bating), without pickle, with 100 parts by weight of water and 12 parts by weight of chromium complex tanning agent dried under mild conditions and described below. These tanning agents are added to the tanning liquor undissolved and in one portion. The usual basification of the chrome tanning is not necessary. The leathers are horsed up after tanning and further processed in the usual way.

Composition of the chrome complex substances used for tanning: 100 parts by weight of a chromic sulphate lye at 33% Schorlemmer basicity, thickened to 18% chromium oxide content, were treated at C. with stirring with (a) 4 parts by weight of anhydrous sodium acetate, or

(b) 10 parts by weight or sodium formate, or

(c) 13 parts by weight of sodium oxalate, or

(d) 6 parts by Weight of glycollic acid (in the form of 70% acid, neutralised with 2.2 parts by weight of sodium hydroxide), or

(e) 11 parts by weight of potassium sulphophthalate, or

(f) A mixture of 4 parts by weight of sodium oxalate and 2 parts by weight of anhydrous sodium acetate.

The chromium complex tanning agents formed after a reaction of several hours are dried under mild conditions.

Example 2 Work is carried out as indicated under (1a)., (1b), (1c), (1d), (1e) or (If) but with addition of 18 parts by weight of undiluted non-spray-dried chrome complex lye to the calf pelts.

A leather is obtained of a quality comparable to that described above.

Example 3 parts by weight of calf pelts are drummed for 6 hours, after preliminary work usually carried out for upper leather (liming, tie-liming, hating, pickling), with 100 parts by weight of water and in each case with 14 parts by weight of the chromium complex tanning agents dried under mild conditions and described below. These tanning agents are added to the tanning liquor in one portion, in an undissolved state. The leathers are horsed up after tanning and further processed without basification and neutralisation in the usual way.

The composition of the chromium complex tanning agents used for tanning is as described under (la), (lb), (10), (1d) or (1 However, 100 parts by weight of the tanning agents dried under mild conditions are mixed with 16 parts by weight of anhydrous sodium carbonate.

We claim:

1. A method of chrome tanning pelts comprising contacting damp pelts with an active amount of a chromium sulphate tanning agent selected from the class consisting of (a) highly concentrated chromium sulphate solution and (b) dried powdered chromium sulphate, the active material having not less than 15% chromic oxide and about .2-.3 mol of coordinatively bound acetic acid radicals per atom of chrome.

2. A process according to claim 1 wherein the tanning agent is added in the undissolved state.

3,174,817 5 6 References Cited in the file of this patent OFlaherty et 211.: Chemistry and Technology of UNITED STATES PATENTS Leather, vol. 2, Reinhold Pub. Corp., New York, 1958,

pp. 250-260. Haslam Sept 5, 1961 Spahrks et 211.: Zeitsehrift Das Leder, v01. 10, No. 7,

OTHER REFERENCES 6 page 145, 1959. Progress in Leather Science, 1920-1945, British XLIH August 1959 Leather Mfgs. Research Assn., London, 1948, pp. 554-555. 

1. A METHOD OF CHROME TANNING PELTS COMPRISING CONTACTING DAMP PELTS WITH AN ACTIVE AMOUNT OF A CHROMIUM SULPHATE TANNING AGENT SELECTED FROM THE CLASS CONSISTING OF (A) HIGHLY CONCENTRATED CHROMIUM SULPHATE SOLUTION AND (B) DRIED POWDERED CHROMIUM SULPHATE, THE ACTIVE MATERIAL HAVING NOT LESS THAN 15% CHROMIC OXIDE AND ABOUT .2-.3 MOL OF COORDINATIVELY BOUND ACETIC ACID RADICALS PER ATOM OF CHROME. 